The present invention relates to an apparatus for producing highly curved sheets of glass.
DE-OS 29 42 738 discloses an apparatus for bending sheets of glass. This apparatus is provided with a horizontal conveyer for transporting the planar glass sheet into a furnace in which the latter is heated to the softening temperature. Disposed after the furnace is a bending station to which is connected, in turn, a separate cooling station for cooling the sheets of glass that were bent in the bending station. The bending station is provided with a lower bending mold and an upper vacuum bending mold. The surfaces of these molds are curved in conformity with the desired shape of the sheet that is to be bent. The lower bending mold can be raised and lowered, and can be removed from a lower mold support in order to be able to adapt and exchange the mold in conformity to various requirements. A change of the mold is required as soon as a different outer contour must be bent, even if this new size has the same radius of curvature as the previously processed sample.
The upper bending mold is embodied as a vacuum bending mold that can be removed from a support plate in order to enable change to another bending mold if differently shaped models are to be produced. Via an annular support member, the bent sheet of glass is then conveyed to the subsequent cooling station, where the cooling process is carried out to achieve tempering of the sheet of glass.
It is a drawback to convey the sheet in the heated state from the bending position into the cooling position while having to leave the bending station. Expensive and complicated transport mechanisms must be utilized that increase the danger of damaging the surface. Furthermore, a temperature loss occurs during the transport process, thereby worsening the breaking pattern due to coarsening. A non-homogeneous breaking pattern can occur. In particular, large-surface sheets of building glass cannot be produced with the heretofore known apparatus.
With the object of providing an apparatus having a high operational efficiency, and which operates without the disadvantageous transport of the sheets of glass from the bending press to a separate cooling mechanism, and which furthermore enables bending within precise tolerances by avoiding the positioning difficulties in the transport mechanism as well as avoiding surface defects, DE-PS 34 07 173 proposed an apparatus for producing highly curved, tempered sheets of glass, especially automotive glass, according to which the bending press is combined with the cooling station, thus eliminating transport of the bent sheets of glass into the cooling station. For this purpose, utilized within the furnace are a vacuum lifting mechanism for raising the softened sheet of glass from the conveyer, and a lower bending mold that can be introduced into the furnace and onto which the softened sheet of glass can be lowered. Provided externally of the furnace is a vertical bending press that cooperates with the bending mechanism that can be moved out of the heating apparatus, and which initially enables the bending and subsequently the tempering of the sheets of glass via coolant connections.
The drawback of this known apparatus is that a complete vacuum lifting station must be accommodated in a hot furnace of approximately 700.degree.. This requires the use of special refractory or high-temperature resistant materials that are extremely expensive; also required is an expensive and complicated construction which can operate in a disturbance-free manner under the aforementioned temperature conditions. Although this technology is controllable and economically usable for the manufacture of automotive glass, this is not possible with large-surface sheet of building glass, for example sheets having the dimensions of 1200.times.2500.times.6 mm. Due to the necessity for having to provide an expensive vacuum lifting mechanism, particular technical problems arise due to the brick that has to be used and which must be coated with a specific refractory material and must furthermore be perforated, so that the lifting process can be carried out in such a way that the glass is not scratched. It is expensive to provide perforations, and to undertake the coating of refractory material that corresponds therewith, without the result being sharp-edged transitions or other irregularities that can lead to damaging of the glass.
A further drawback is that the bending mechanism must be capable of being introduced into the furnace, since during the retention time in the furnace the bending mechanism is heated up, which adversely affects the subsequent cooling in the cooling station. Here also special refractory materials must be used.
Up to now, all of these drawbacks have made it impossible to carry out the production of highly curved, tempered, large-surface sheets of building glass with such an apparatus.
In view of this state of the art, it is an object of the present invention to provide an apparatus having a high operational capacity for producing highly curved, tempered, large-surface sheets, especially sheets of building glass, with this apparatus, while avoiding the aforementioned drawbacks, operating at reduced capital expense and therefore being cheaper, and also making it possible to bend and cool sheets, after they have been heated up, without complicated manipulations.